Random 401 unauthorized on css js files on net 4 8 asp net website hosted on ii

ASP.NET is a widely used programming language for developing web applications. It provides a powerful framework for building websites and web services. However, like any other programming language, ASP.NET can encounter issues that need to be addressed. One common problem that developers may face is the occurrence of random 401 unauthorized errors on CSS and JS files.

When a website is hosted on IIS (Internet Information Services), it is responsible for handling HTTP requests and serving the requested files. The 401 unauthorized error indicates that the user making the request does not have the necessary permissions to access the requested resource.

To solve this issue, there are a few steps that can be taken. First, it is to ensure that the necessary permissions are set correctly for the CSS and JS files. This can be done by checking the file permissions in the file system and granting the appropriate access rights.

Step 1: Check File Permissions

Open the file explorer and navigate to the where the CSS and JS files are stored. Right-click on the files and ”. In the properties , go to the “Security” tab and check if the necessary permissions are set for the files. If not, click on “Edit” and add the required permissions.

If the file permissions are already set correctly, the next step is to check the IIS .

Step 2: Check IIS Configuration

Open the Internet Information Services (IIS) Manager and navigate to the website in question. Right-click on the website and select “Properties”. In the properties window, go to the “Directory Security” tab and click on “Edit” under the “Authentication and access control” section. Make sure that the appropriate authentication methods are enabled and configured correctly.

If the file permissions and IIS configuration are both correct, the issue may be related to the ASP.NET application itself.

Step 3: Check ASP.NET Configuration

Open the web.config file of the ASP.NET application and look for any settings related to authentication and authorization. Ensure that the correct authentication mode is set and that the necessary authorization rules are in place. You may also need to check if any custom authentication or authorization modules are causing the issue.

If none of the above steps solve the problem, it may be helpful to enable detailed error in order to get more information about the cause of the 401 unauthorized error.

Step 4: Enable Detailed Error Messages

In the web.config file, locate the section and add the following lines:


By enabling detailed error messages, you will be able to see the exact error that is occurring, which can help in troubleshooting and finding a solution.

In conclusion, random 401 unauthorized errors on CSS and JS files in an ASP.NET website hosted on IIS can be resolved by checking file permissions, IIS configuration, ASP.NET configuration, and enabling detailed error messages. By following these steps and making the necessary adjustments, you can ensure that your ASP.NET application runs smoothly and users can access the required without any issues.

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